1. Field of the Invention
The present invention relates to improvements in a resonator device for a high-pressure fuel pump.
2. Background of the Invention
In FIG. 6, there is shown a sectional view of a conventional resonator device. In FIG. 6, reference numeral 1 designates a high-pressure fuel pump which is attached to an engine wherein injection is made in a cylinder. Reference numeral 18 designates a casing of the high-pressure fuel pump, and which has a storing recess 18d formed therein. Reference numeral 22 designates a passage at a discharge side of the high-pressure fuel pump 1, which is formed in the casing. Reference numeral 29 designates a cover which is fixed to the casing 18 and formed in a lidded shape. Reference numeral 30 designates a cap which is fixed to the casing 18 between the casing 18 and the cover 29 by a bolt 31, which provides a fuel passage chamber 32 together with the storing recess 18d in the casing 18 and a volume chamber 33 together with the cover 29, and which has an orifice 30b formed therein to communicate between the fuel passage chamber 32 and the volume chamber 33. Reference numeral 30a designates a fixing portion of the cap 30 which is to be screwed with the bolt 31. Reference numeral 34 designates a sealing material which is arranged between the cap 30 and the casing 18. Reference numeral 35 designates another sealing material which is arranged between the cap 30 and the cover 29. Reference numeral 36 designates the resonator device constituted by these elements as a whole.
In the conventional device thus constructed, the high-pressure fuel pump 1 is driven to inject a fuel into the discharge side passage 22. The reciprocation of the piston in the high-pressure fuel pump 1 causes intake strokes and exhaust strokes to be repeated in the high-pressure fuel pump 1, generating pressure pulsations in the discharge side passage 22 forming a part of a fuel pipe.
In order to damp the pressure pulsations in the fuel in a predetermined frequency range, the fuel passage chamber 32 and the volume chamber 33 have been provided, and both chambers have been communicated together through the orifice 30b having a predetermined length and a predetermined diameter.
The frequency of the pressure pulsations which can be absorbed by the resonator device is defined as follows: ##EQU1## wherein f represents a frequency, c represents the speed of sound (in a liquid), s represents a cross-sectional area of the orifice 30b, l represents the length of the orifice 30b, and v represents the volume in the volume chamber 33.
In the conventional resonator device, the outer diameter .phi.B of the cap 30 on a side of the fuel passage chamber 32 is the same as the outer diameter .phi.A of the cap 30 on a side of the volume chamber 33.
When the pressure difference between the fuel passage chamber 32 and the volume chamber 33 is generated in alternately opposite directions in the conventional device, loads are applied to the cap 30 in alternately opposite directions accordingly.
Such a phenomenon will be described in reference to FIGS. 7-9.
In FIGS. 7-9, reference P1 represents a pressure which is generated on the cap on the side of the volume chamber 33, reference P2 represents a pressure which is generated on the cap on the side of the fuel passage chamber 32, reference F1 represents a load which is applied to the cap on the side of the volume chamber 33, and reference F2 represents a load which is applied to the cap on the side of the fuel passage chamber 32.
As shown in FIG. 9, the cap 30 has great loads alternately applied thereto, causing the cap 30 to be vibrated. The vibration of the cap 30 has created a problem in that the sealing materials 34 and 35 are worn.